Sigtronics SPA-4Si - Manual (Page 6)

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In most aircraft the squelch controls will not need to be set again unless
you change the number or type of headsets used with the system. In some
high noise aircraft it is better to set the squelch during climb or cruise.
VOLUME SETTING - The Volume controls should be set to the minimum
level for best performance. Intercom Volume levels set too high allow exces-
sive background noise to enter the headset. This promotes whispering
into the headset microphone. Excessive background noise and whispering
combine to degrade what is called the “signal to noise ratio”. This decreases
intelligibility and interferes with proper Squelch (VOX) operation.
RADIO TRANSIT MODE
Because of the dual intercom design of the Sigtronics Dual Bus Kit,
transmitting from both pilot and co-pilot positions is possible simultaneously
or one-at-a-time. Each pilot selects the radio he wishes to use via his audio
panel. When he presses his PTT switch, his headset mic is routed through the
intercom to the radio he selected. Only his mic will be live. The microphone
of any passengers connected to the pilot’s side of the system (i.e. the pilot’s
SPA-4Si) will be muted when the pilot transmits. Similarly, when the co-pilot
transmits, only the co-pilot’s mic signal will go out on the radio selected
by the co-pilot. When transmitting, the pilots will hear their own voice via
the aircraft radio side-tone return. If the radio does not provide transmit
side-tone, then they will not hear their voice when transmitting.
RADIO MONITORING
Radio monitoring is automatic. The radio monitor circuit is always active;
even with the SPA-4Si unit power switch “OFF”. Each pilot will only hear the
radio selected by his respective audio panel.
MUSIC OPERATION
Music is controlled at the music source itself. To adjust the music volume
level set the volume control on the music source. Similarly, to turn on or
off the music use the appropriate control on the music source. When the
music source is “ON” the SPA-4Si system automatically mutes and restores
the music to the headsets at the appropriate time. The SPA-4Si default
mode of operation is to partially mute during intercom conversations and
full mute during any aircraft radio communications
MUSIC MUTE OPTIONS
MUSIC MUTE LEVEL DURING ICS - During normal intercom operation
there are two possible muting levels, full or partial. Partial mute is the factory
default. Alternately, “full mute” mode is user selectable prior to intercom
installation. Note: during radio transmission and reception, the music will
always full mute. This is for communication safety reasons.
SOLO FLIGHTS
Since the intercoms are not needed during solo flights, they may be turned
to the “OFF” position. The pilot will still hear the aircraft radio(s), since this
circuit is always active, and may transmit to ATC via his headset and push-to-
transmit switch. To hear music, the intercom will have to be in the “ON” mode.
FAIL-SAFE
I f power to the SPA-4Si units fails, the pilots can still transmit and receive on
the aircraft radio(s) (assuming the radio(s) are still functioning). If a problem
is ever suspected, switch the intercoms “OFF”. In this mode you will still be
able to transmit and receive on the aircraft radio(s) from the pilot’s position.
If the radio does not provide sidetone, then the pilot will not hear his voice
in this “FAIL-SAFE” or “OFF” mode.
STEREO MUSIC SYSTEMS
Most automotive stereo units operate from 12V-14V sources. If you want to
use a 12 volt music source in a 28 volt aircraft do not connect them directly
to power. Regulators or converters are available to permit operation from
24V-28V sources.
Some AM-FM music receivers are capable of causing interference with
aircraft COM and NAV receivers. The aircraft panel should be placarded
accordingly. Most player only units (MP3 or CD) do not cause interference
with aircraft receivers.
Line level stereo music outputs can also be used into the SPA-4Si system.
Some line level outputs however, are a fixed level and are not adjusted by
the devices volume control. If this is the case you will not be able to change
the volume of the music you hear in the headsets. Headphone level or
Speaker level outputs would be better in this case.
STEREO HEADSETS
The Sigtronics Dual Bus Kit systems are designed for use with general avia-
tion Stereo headsets with high impedance speakers (300 to 600 ohms).
Headsets with low impedance (less than 100 ohms) speakers should not
be used with SPA-4Si systems intercoms without modification. Contact
Sigtronics for details. In general, headsets with speakers of high and low
impedance and / or unmatched audio efficiencies should not be used
together without modifications.
Sigtronics stereo headsets are specifically designed for the aircraft high
noise environment and give excellent noise attenuation. They also pro-
vide full frequency response stereo for maximum enjoyment. They are
compatible with aircraft mic circuits and can be used as general aviation
headsets in aircraft that are not equipped with stereo headphone jacks.
This is because they include a switch to change from “Stereo” to “Monaural”.
No adapters required.
NOTE: General aviation headset (monaural) phone plugs should not be
plugged into SPA-4Si stereo phone jacks. A monaural plug in a stereo jack
shorts out one of the audio channels. This will not damage the SPA-4Si units
in any way but will cause reduced performance. General aviation headsets
may be used only if one of the following three changes are made:
1. Monaural to stereo adapters are used on the headset headphone plugs.
(Only monaural music will be heard.)
2. The general aviation headsets are re-wired for stereo reception.
3. Install the Sigtronics SPA-4Si units for monaural operation. See note 7
in the “WIRING INSTRUCTIONS” section on page 4.
Sigtronics Corporation
178 East Arrow Highway
San Dimas, CA 91773
(909) 305-9399
www.sigtronics.com
spa4si_ins.pdf SPA4SiInst P/N 700141 2-1-2012
FAA TSO: C50b ENV. CAT (DO-160) CFBBBX